For the dressing of cylindrical grinding worms for the continuous generation grinding of gears in the module range of 1 to 3 mm, gang rolls or full profile rolls are often employed which enclose the desired grinding worm profile over one or more threads. One such tool is known e.g. from CH 686 171 A5, which by a special construction permits the re-machining of the diamond coating of a composite diamond dressing tool for dressing both threads of a two-start cylindrical grinding worm.
Especially in the case of workpiece teeth with a module of less than 1 mm, however, so-called full profile rolls with 3 to 5 profile ribs are used which, in similar manner as a thread dressing roll, simultaneously enclose 3 to 5 adjacent threads of the total grinding worm profile. Such a profile roll is shown in FIG. 1 in mesh with a grinding worm.
A disadvantage of these full profile rolls is that a re-machining of the abrasive coating to correct the flank geometry and to assure adequate surface quality of the ground gears is as yet technically unattainable, and that they must therefore be produced by the very expensive and time consuming negative or reversal process. This means that towards the end of the dressing process the grinding worm threads must be brought one after the other into mesh with several different profile ribs of the dressing tool without further dressing infeed, in order to reduce the effective roughness depth of the grinding worm flanks to the permissible value and to “calibrate” the profile.
For the continuous generation grinding of fine and ultra-fine teeth in the module range up to 1 mm, multi-start grinding worms with more than 5 starts are generally employed. For such grinding worms the well known above mentioned full profile rolls have an inadequate number of ribs available to profile all the grinding worm threads simultaneously, i.e. in the same dressing stroke. For this reason, to produce all the grinding worm threads of these grinding worms when pre-profiling, the profile roll must be put into action axially displaced several times. FIG. 2 shows a three-ribbed profile roll 2 in a first axial dressing position Y1 in a first, second (Y1′) and third (Y1″) grinding worm revolution of a five-start grinding worm with a lead H for producing the first three of the five grinding worm threads. To pre-profile the two remaining grinding worm threads the profile roll is brought to a second dressing position Y2 and Y2′, which is axially displaced by two profiling ribs relative to the first dressing position Y1, Y1′, Y1″. Since the number of grinding worm starts and the number of ribs on the profile roll are not of an integer ratio, the profile rib flanks of the dressing tool are subject to unequal wear due to unequal use, which causes losses in accuracy when subsequently finish profiling.
Another disadvantage of the number of profile ribs being less than the number of grinding worm starts is that the ribs provided on the dressing tool must perform both the pre-profiling work and the finish profiling work. This means that the quality of the finish profiling, i.e. the calibration quality is impaired by the far greater wear of the abrasive coating during pre-profiling.
The disadvantages mentioned above make it apparent that the known full profile rolls with 3 to 5 profile ribs are unsuitable for the profiling of multi-start small moduled grinding worms.
Furthermore in the generation grinding of fine teeth as opposed to the grinding of large moduled workpieces it is usual, when changing over to a new workpiece, to remove the grinding worm profile no longer required, and to profile the grinding worm completely freshly. Since the abrasive profile of the known profile rolls is not suitable for the stripping or removal of the grinding worm profiles no longer required, a separate tool suitable for this expressed purpose must be provided on the machine, or the grinding worm must be removed from the machine to strip it, which makes breaking down and fresh setting up necessary.